no 



MENDELISM 



CHAP. 



tory factor owing to the repulsion between these factors. 

 The nature of the F2 generation in each case is in har- 

 mony with the above scheme. As, however, it serves to 

 illustrate certain points in connection with intermediate 

 forms we shall postpone further consideration of it till we 



discuss these matters, and 



[9]FfppIi 



ffPPii [^] 



for the present shall limit 

 ourselves to the explana- 

 tion of the different be- 

 haviour of the Fi males 

 and females when crossed 

 with the Brown Leghorn. 

 And, first, the cross of 

 Brown Leghorn female by 

 Fi male. The Brown Leg- 

 horn hen is on our hy- 

 pothesis FfppIi, and produces gametes Fpi and fpl. 

 The Fi cock is on our hypothesis fJPpIi, and pro- 

 duces in equal numbers the four kinds of gametes 

 JPI, fPi, fpl, fpi. ■ The result of the meeting of these two 

 series of gametes is given in Fig. 24. Of the eight differ- 

 ent kinds of zygote formed only one contains P in the 

 absence of /, and this is a female. The result, as we have 

 already seen, is in accordance with the experimental facts. 

 On the other hand, the Brown Leghorn cock is on our 

 hypothesis ^/j;^//. All his gametes consequently contain 

 the inhibitor factor, and when he is mated with an Fi 



